For instance, silicon-based solar cells, used in general practice, have been formed in structures wherein a silicon substrate, composed of a p-type multicrystalline semiconductor, has: an upper surface provided with an anti-reflection film and a light-receiving surface electrode formed via an n+ layer; and a lower surface provided with a rear surface electrode via a p+ layer (hereinafter, these electrodes will be merely referred to as “electrodes” unless otherwise specified). The anti-reflection film serves to decrease a surface reflection rate while keeping an adequate visible light transmission rate and includes a thin film composed of silicon nitride, titanium dioxide and silicon dioxide, etc.
The light-receiving surface electrode of the solar cell is formed in a process referred to as, for instance, fire through. In such an electrode forming method, for instance, the anti-reflection film is formed on the n+ layer over an entire surface thereof, after which a conductive paste is coated on the anti-reflection film in a suitable shape using, for instance, a screen printing method and, subsequently, firing treatment is conducted. With such a method, steps become simpler than those of a case wherein the anti-reflection film is removed in part and an electrode is formed in such a removed area, an issue of a positional misalignment between the removed area and an electrode forming position does not occur. The conductive paste has a principal composition including, for instance, silver powder, glass frit (flake-like or powder-shaped glass fragments obtained by melting glass raw materials, quenching the melted glass and crashing the quenched glass depending on needs), an organic vehicle and an organic solution. In a firing process, the glass components, present in the conductive paste, break the anti-reflection film by etching, resulting in the formation of an ohmic contact between a conductive component, present in the conductive paste, and the n+ layer (see, for instance, Patent Publication 1).
With such a light-receiving surface electrode forming method, accordingly, it has been found desirable to improve the ohmic contact as well as increasing Fill Factor (FF) and energy conversion efficiency. To realize these, various attempts have been made in the art to perform improvements for increasing fire through properties.